Veteran is spreading awareness and letting neighbors know about PTSD veterans and fireworks with this poster on the Military with PTSD Facebook page. (Military with PTSD Facebook)

A reminder of war's lasting effect flashed across social media today as a photo of a veteran standing behind a sign expressing concerns about fireworks and the emotional trigger of nearby explosions spawned an outpouring of reaction.

In less than 24 hours, more than 100,000 people shared the Facebook post, many of them veterans acknowledging the challenges of neighbors shooting off fireworks without thinking of the consequences of those nearby.

"Combat veteran lives here, please be courteous with fireworks," reads the poster held by a bearded veteran in the photo that went viral Tuesday and Wednesday.

"It's a nice statement that people are picking up and sharing that," says Barbara Van Dahlen, a Washington, D.C. area psychologist and founder of Give An Hour, which provides free behavioral health counseling to troops, veterans and their families.

"The sensitivity here is that if you know that your next-door neighbor served ... and you're planning to have a fireworks display in your backyard, it's probably the thoughtful thing to do to let them know," she says.

Emotional reactions to loud noises or sounds that bring memories of traumatic events can be very common among veterans and non-veterans, she says. In the most severe cases, where these reactions or memories are strong a recur over time can they amount to a diagnosis of post-traumatic stress disorder.

In either case, she says, the concern is not that a veteran might react violently, but that the fireworks "could send somebody into a very painful, stressful, emotional experience remembering a firefight or a buddy who was killed."

Research findings differ, but an estimated 7 percent to 20 percent of the more than 2.5 million veterans and troops who have served in Iraq and Afghanistan are believed to have developed PTSD.

The disorder is characterized by emotionally re-experiencing or remembering traumatic events, the thoughts involuntarily triggered for combat veterans by the sound of an explosion or gunfire, or even certain sights and smells, according to a recent report by the Institute of Medicine.

This can cause a variety of reactions, including altering mood or triggering hyper-vigilance or a need to avoid people and places, the report says.

Combat veterans are not the only sufferers of PTSD, the illness occurs after other types of experiences such as a sexual assault or a car accident.

"Post-traumatic stress disorder is one of the signature injuries of the U.S. conflicts in Afghanistan and Iraq, but it affects veterans of all eras," the report says.